Musical instruments, such as the strings, horns, brass, woodwinds, and percussion of the modern orchestra and the multitude of other non-western instruments from around the world have been known for centuries. Conventional musical instrument development has attempted to create new behaviors and new sounds, from both a purely acoustic and electroacoustic perspective. For example, modern guitars have developed significantly since the early invention of the first guitar. Similarly, the invention of the synthesized drum or drum machine provided an entirely new palette of sonic options.
In an electroacoustic musical instrument, a substantially acoustic signal is converted to an electric representation of that signal and then manipulated by electronic devices. An electro-acoustic example would be an electric guitar which has the ability to encode the acoustic vibrations of a string into an electrical signal via an electromagnetic pickup. The resultant electrical signal may then be routed through any number of electrical devices that purposely affect the electrical signal to create new sounds.
One such new sound, for example, would be the tremolo sound effect, which is now a common musical effect. The acoustic tremolo effect is a flutter-like effect that alters the frequency of the affected tone by some arbitrary modulation, which is typically produced by mechanical or electromechanical induction of a tremolo effect via acoustic amplitude frequency or phase modulation. The acoustic tremolo sound effect can be achieved by applying a mechanically induced modulation with first the Hammond Tone Cabinet (D-20) and later the Leslie Speaker (see U.S. Pat. No. 2,450,139 by Hartsough, and U.S. Pat. No. 3,014,192 by Leslie). The acoustic tremolo effect has some limitations, in that; the frequency range of the modulator is limited to low frequency oscillation below 100 Hz. Other well-known analog circuit effects can be produced through a combination of transistors, capacitors, amplifiers, inductors, and other suitable electrical and/or electronic devices.
Another example of an electro-acoustic development is a sound synthesizer or an electronic musical instrument that generates electric signals that are converted to sound through instrument amplifiers and loudspeakers or headphones. U.S. Pat. No. 4,018,121, by Chowning (hereinafter “Chowning”) discloses frequency modulation (FM) for musical sound synthesis. The popularity of the sound synthesizers in popular music resulted in the development of digital modular synthesizers and digital software synthesizers, which resulted in a move away from analog electric musical instruments. In some embodiments, the input signals are generated by a computer system, based on mathematical and physical models of known acoustic systems or methods of digital signal processing (see U.S. Pat. No. 6,049,034 by Cook).
An example of an acoustic instrument electromagnetic (EM) augmentation is the control for musical instrument sustainers, or E-Bow, (see U.S. Pat. No. 6,034,316 by Hoover). This device amplifies feedback with an electromagnet to vibrate ferromagnetic strings and sustain the tones continuously.
An example of an acoustic instrument electromagnetic (EM) incorporated directly into the design of an electric instrument is the Rhodes piano (see U.S. Pat. No. 3,418,417A by Rhodes and DE2,264,786A1 by Rhodes) This device utilizes single-tine tuning forks to generate tones, which are picked up by a transducer that converts the vibrations into electrical signals, and then connected to an amplifier and a speaker and amplified
Another example of an acoustic instrument that has been augmented with electronics is a magnetic resonator piano as described by McPherson & Kim [Augmenting the Acoustic Piano with Electromagnetic String Actuation and Continuous Key Position Sensing, 2010. In NIME (pp. 217-222)] or the Rhodes piano, which uses a single-tine fork driven by an electromagnet. Other examples include the overtone fiddle and the feedback resonance guitar (see [Advancements in actuated musical instruments. Organised Sound, 16(2), p 154-165 by Overholt, Berdahl, and Hamilton, 2011]). There currently lacks technology that allows the flexibility of modulation found on sound synthesizers on acoustic or augmented acoustic instruments. This invention bridges this gap between electronic and acoustic methods of synthesizing sound through intermodulation and frequency modulation.
An acoustic modification or augmentation of a sound reproduction system is also possible. U.S. Pat. No. 1,346,491 discloses example acoustic amplification and filtering using a waveguide or horn to increase the loudness and directionality of the sound signal.
Chowning's seminal work drew inspiration from the spurious frequency products found from frequency modulation in radio engineering. Similarly, spurious frequency products called intermodulation products typically warrants mitigation, for instance in speaker design (see U.S. Pat. No. 3,327,043A, by Martin). Recently intermodulation has been utilized in the field of Dynamic Atomic Force Microscopy (see U.S. Pat. No. 8,849,611 by Haviland et al.). Expanding frequency content rather than reducing it, rich frequency content can be produced.